Safety device for an airbag-system

ABSTRACT

A safety device for an airbag-system which has not been triggered by an accident, comprising a fabric which is suitable for surrounding a steering wheel of a motorcar which is provided with the airbag-system. The fabric is suitable for tightening at the side of the steering column on which the steering wheel is mounted, such that if the airbag-system is activated during a rescue operation, inflation of the airbag is hindered by the fabric.

The present invention relates to a safety device for an airbag-system.

It is known from the Dutch newspaper De Volkskrant of Oct. 3, 1995, thata good 25 years ago already an airbag was designed which would instantlypop out from the middle of the steering wheel of a motorcar the momentsensors in the motorcar perceive a collision. Such airbags preventserious injuries to occupants of the motorcar, especially if they werenot wearing a safety belt at the time of the collision. Actually,airbags are still subject to constant development, taking better intoaccount the kind of collision and the situation in which the occupantsof the motorcar find themselves at the moment of the collision andinflation of the airbag.

Practical experience has shown, however, that after an accident orcollision one may face the problem that the airbag is not yet activatedand assistance to the occupants takes place while the risk exists thatthe airbag will still inflate. This is a danger for both the helpers andoccupants needing assistance.

To avoid this problem, an airbag retention device has been proposed inU.S. Pat. No. 5,277,440. From this document, it is known to apply agenerally round sheet of flexible material having a diameter slightlylarger than the steering wheel or at least approximately the same sizeas the steering wheel. The device also comprises a plurality ofcriss-crossed strips, preferably of a reinforced nylon material, eachattached to one another at a central point. Each of the stripsterminates in a closed loop and a cord or drawstring passes through eachof the closed loops of each of the strips. In such a device, thepressure build-up during inflation of the airbag is enormous and noguarantee exists that the cord or drawstring will be able to withstandthe pressure build-up.

It is therefore preferred in the known safety device to have thedrawstrings pass through each loop twice, i.e. twice around theperiphery of the strips to provide additional restraining strength. Whenthe safety device is placed over the steering wheel, the drawstring orcord may be pulled tightly to pull the end loops of each of the stripstowards to each other so as to form an opening having a smaller diameterthan the diameter of the steering wheel, and in order to provide a tightfit of the restraining fabric around the steering wheel. However, whenthe drawstring is tightened, the opening is only slightly smaller thanthe diameter of the steering wheel.

This aspect in combination with the huge pressure build-up duringinflation of the airbag renders this system unreliable when repeatedlyused or even when used only once in retaining an inflating airbag.

It is the object of the invention therefore to provide a reliable safetydevice for an airbag-system which can be safely used on any sizesteering wheel and repeatedly.

To this end, the safety device according to the invention ischaracterized in that a space of 10 to 15 cm is left between thesteering wheel and the fabric fitted around it. Contrary to any teachingin the prior art, every tight fit of the fabric is therewith avoided,and in the case of untimely inflation this leaves the airbag sufficientspace for a controlled pressure build-up.

The fabric can be secured particularly effectively around the steeringwheel if the cord or the ribbon for gathering the outer edge isconnected at a first extremity with the outer edge of the fabric and isprovided at a second extremity with a hook means for the detachableconnection of the second extremity to a permanent point. The chosen hookmeans may, for instance, be a securable carabine hook such as the clogscrewgate kind, which has a tensile strength of about 2400 kg.

In a first embodiment of the safety device according to the invention atleast part of the fabric takes the form of a meshed net. The dimensionsof the net may vary. However about 9×9 cm has been shown to be apreferred mesh size. This provides the airbag with enough space to allowit to still extend somewhat through the mesh of the net, so thattensions of too great a force in the cords of the net are avoided.

The net can be made sufficiently strong by using aramide cords having adiameter of about 7 to 8 mm. Of course, other cords providing sufficienttensile strength are also possible, but especially the use of aramideprovides a lightweight, yet strong product which is quite suited for theintended safety function. Moreover, this function is maintained over anextensive temperature range.

In another embodiment of the safety device according to the invention atleast part of the fabric is closely woven and is provided with one ormore openings near the outer edge. In general, using a closely wovenfabric affords the advantage of halving the sound pressure produced byan activated airbag. The sound pressure of an exploding airbag rangesfrom 120-150 dB. In addition, very adequate protection is providedagainst dust production caused by the exploding airbag, which wouldotherwise cause irritation of the eyes. One may choose, for instance, tomake the fabric from the fire-resistant Nomex III® material made by TenCate Protect B.V., Nijverdal, or from metal. Further, when using afabric, it is desirable to reinforce the openings which serve to limitthe pressure build-up when the airbag is activated, by means of,preferably metal rings. A very favourable embodiment is characterized inthat at least part of the fabric is formed from closely woven aramidefibres such as, for instance, Kevlar®. Apart from the above-mentionedadvantages for using aramide there is the further advantage that thefabric—though closely woven—is gas-permeable, affording better controlof the pressure build-up from the airbag.

The invention will now be further elucidated with reference to thedrawing in which

FIG. 1 shows a first embodiment of the safety device according to theinvention in the spread out state;

FIG. 2 shows the safety device in the first embodiment according to theinvention fitted around a steering wheel of a motorcar before inflationof the airbag;

FIG. 3 shows the safety device in the first embodiment according to theinvention fitted around a steering wheel of a motor car after inflationof the airbag;

FIG. 4 shows the safety device in a second embodiment according to theinvention in the spread out state; and

FIG. 5 shows the safety device in a third embodiment according to theinvention in the spread out state.

Corresponding parts are indicated by the same reference numbers.

FIG. 1 shows a safety device according to the invention comprising a net1 provided with mesh 2. The shape of the net 1 is round and its outeredge is provided with a cord 3 which preferably is attached at oneextremity 4 to the net 1, and is provided at the other extremity 5 witha hook means 6 for the detachable connection of this second extremity 5to a permanent point.

As shown in FIG. 2, the net 1 is fitted over the steering wheel 7 andtightened at the side of the steering column 8 by drawing tight the cord3 which, in order to secure the net 1 around the steering wheel 7, maybe wrapped several times around the steering column 8 and be fastened bymeans of the hook 6 into one of the loops 9 or a mesh 2 of the net 1.

FIG. 3 shows the situation where the airbag 10 has been activated andthe net 1 envelopes the airbag 10, while the airbag 10 can be seen toform bulges 11 through the mesh 2 of the net 1. In this situation, thespace between the net 1 and the steering wheel 7 is maximally 10 to 15cm. Making the net 1 from aramide cords having a diameter of about 7 to8 mm, provides a reliable safety device which can also be used underfire-hazardous conditions due to the fact that aramide retains itstensile strength over a wide temperature range. The hook means 6 ispreferably a securable carabine hook of the clog screwgate kind, whichhas a tensile strength of about 2400 kg.

FIG. 4 shows a second embodiment of the safety device according to theinvention, in which the fabric in its totality is closely woven and isprovided with openings 15 near the outer edge. This closely woven fabriccan thus be fitted over the steering wheel like a sack. The fabric maybe made from fire-resistant Nomex III® material or possibly from metal.With Nomex III® or other fabric the openings 15 are preferably to beprovided with metal rings for reenforcement. By employing openings 15,the pressure build-up on activation of the airbag is controlled and doesnot reach such high values as when such openings are not employed. Theclosely woven fabric 12 may also be made from aramide fibres, forinstance from Kevlar®. This has the advantage that the openings 15,though useful, are less crucial, because such an aramide fabric isgas-permeable.

FIG. 5 shows a third embodiment of the safety device according to theinvention, namely a combination of the embodiments shown in FIG. 1 andFIG. 4. In this embodiment part 14, which will be positioned over thesteering wheel, is executed as closely woven fabric in order to retainthe best possible protection against dust for the benefit of both theoccupants of the motorcar and the helpers, which protection is optimalin the embodiment according to FIG. 4. The part 13 surrounding theclosely woven part 14 of the fabric takes the shape of a net as shown inthe embodiment of FIG. 1. Thus, in addition to the good protectionagainst dust, this embodiment offers very adequate control of thepressure build-up.

What is claimed is:
 1. A safety device for an airbag-system,characterized in that the safety device comprises a flexible fabricsurrounding a steering wheel of a motorcar provided with theairbag-system, and suitable to be tightened at the side of a steeringcolumn on which the steering wheel is mounted, such that when theairbag-system is activated, inflation of the air-bag is hindered by thefabric, wherein an outer edge of the fabric comprises a structureselected from the group consisting of cords and ribbons for narrowingthe outer edge of the fabric, characterized in that a space of 10 to 15cm is left between the steering wheel and the fabric such that thesafety device hinders expansion of the airbag, while the space provideslimited expansion to prevent an explosion of the airbag.
 2. A safetydevice according to claim 1, characterized in that a first extremity ofthe structure is connected with the outer edge of the fabric and in thatsaid safety device additionally comprises a hook means for detachableconnection of a second extremity of the structure to a permanent point.3. A safety device according to claim 1 characterized in that at leastpart of the fabric comprises a meshed net.
 4. A safety device accordingto claim 3, characterized in that the meshed net is approximately 9×9 cmin size.
 5. A safety device according to claim 3 characterized in thatthe meshed net comprises aramide cords having a diameter of about 7-8mm.
 6. A safety device according to claim 1 characterized in that atleast part of the fabric is closely woven and near the outer edgecomprises one or more openings.
 7. A safety device according to claim 6,charactered in that the openings are reinforced by metal rings.
 8. Asafety device according to claim 1 characterized in that at least partof the fabric comprises closely woven aramide fibres.